Ultraviolet (UV) lamp systems are commonly used for heating and curing materials such as adhesives, sealants, inks, and coatings. Certain UV lamp systems have electrodeless light sources and operate by exciting an electrodeless plasma lamp with microwave energy. In an electrodeless UV lamp system that relies upon excitation with microwave energy, the electrodeless plasma lamp is mounted within a metallic microwave cavity or chamber. One or more microwave generators, such as magnetrons, are coupled via waveguides with the interior of the microwave chamber. The magnetrons supply microwave energy to initiate and sustain a plasma from a gas mixture enclosed in the plasma lamp. The plasma emits a characteristic spectrum of electromagnetic radiation strongly weighted with spectral lines or photons having UV and infrared wavelengths.
To irradiate a substrate, the UV light is directed from the microwave chamber through a chamber outlet to an external location. The chamber outlet is capable of blocking emission of microwave energy while allowing UV light to be transmitted outside the microwave chamber. A fine-meshed metal screen often covers the chamber outlet of many conventional UV lamp systems. The openings in the metal screen transmit the UV light for irradiating a substrate positioned outside the RF chamber; yet substantially block the emission of microwave energy. In some conventional UV lamp systems, a shutter also covers the chamber outlet and is selectively operable to expose the substrate to the UV light.
Some applications of the UV lamp systems require very precise intensities of UV light. These applications are sensitive to changes in the UV light intensity, requiring the light intensity to be substantially constant. Providing a substantially constant UV light intensity presents some challenges. Conventional methods of measuring UV light intensity utilize UV intensity sensors that are placed below the light source. These sensors measure the UV light intensity of the light source once and cannot indicate the UV light intensity from successive applications without interrupting the use of that light source. Moreover, such sensors are often prone to solarization due to the constant exposure to high intensity UV light, rendering them inoperable. Still further, such methods are typically performed by the lamp system customer or the lamp system vendor during setup and/or maintenance, which are disruptive to the use of the UV lamp systems. Such methods also require significant time by the customer to configure future UV intensities that can be used for their applications that will “degrade gracefully” as those UV lamp systems decrease in their intensity.
Operators of the UV lamp systems therefore often use preventative maintenance and bulb replacement schedules in an attempt to ensure a high level of process control, as automated performance detection and control systems that take into account UV light intensity are not available. But these maintenance schedules also significantly interrupt the use of the UV lamp system, because any processing of substrates is halted to perform any maintenance or testing. Moreover, these maintenance schedules generally fail to take into account and adjust for degradation and/or contamination of the UV lamp system between various applications and/or substrates. This is often a problem for applications that require a high degree of consistency.